Recording material



Patented Aug. 2 2, 1950 UNITED STATES PAT ENT OFFICE to Arthur D. Little, Inc., Cambridge, Mafia; a. corporation of Massachusetts No Drawing a nseprember 6,1947 Serial No. 772,597

6 Claims.

Data supplied by measuring instruments or all typescan be recorded onstrips or sheets or paper or other suitable material which carries a superficial layer of a material which, upon pressurable contact with a stylus, is wholly or partially compacted or removed from the suitably colored support. It has been proposed to use for this purpose dark paper strips covered with a so-called blushed-film which uponpress-urable contact with an object loses its light colored and opaque appearance and shows the dark paper surface therebehind. The paper strips can thus be used to receive a continuous record applied by means of a, pressure stylus. Recording material of this type however is not suitable for certain purposes, particularly when the strip has to be repeatedly handled, which usually involves pressurable contact with objects other than the recording stylus, so that the record becomes obscured or disfigured with spots or marks rendering its interpretation difficult or impossible.

It is an object of the present invention to provide a; recording material of the blush-ed film type which is very little senstive to pressurean'd therefore can be handled without particular attention to record obscuring disfigura'tion through accidental contact. Another object is to provide a recording material of the above mentioned type whose blushed film is aiiected for intended recording purposes upon contact with a heated recording stylus rather than pressure exerted thereon, whereby the optimum temperature can be adjusted to suit given requirements such as stylus construction. Still another object of the invention is to provide material of this type which is inexpensive, easy to manufacture, durable, quite insensitive to pressurable contact but easily responding to a heated recording element, and which has good keeping qualities. Recording paper of this type is particularly suitable for purposes of electrocardiographs because they avoid the usual photographic processes heretofore used in this field. In electrocardiography, it is particularly important that the record strips can be handled quickly and without regard to their susceptibility torunavoidable pressurable contact with the hospital or sickroom environment,

In its main aspect, the invention consists in applying to a support such a strip of paper a very thin coat of blushed film of a color contrasting with that of the support, applied from solution of a film forming material in a volatile solvent, the solvent being compatible with water having considerably higher vapor pressure than water, this film having only iittle sensitivity to" pressure but considerable and adjustable sensitivity' to heat; this reduced sensitivity to pressure and adjustably increased sensitivity to heat is due, in accordance with other aspects of the invention, to the exclusionfrom the blushed film of any softening admixture or of such admixtures other than a primary plasticizer, to the use of primary plasticiaers having a; vapor pressure lower than approximately that of diethylphthalate, and. to the use of pnmary plasticizers, that is plasticizers which are solvents for the film forming material. an additional aspect, the invention permits predetcrrnihation of the effective stylus temperature sufllcient for satisfactory recording, by adjusting the admixture including omission-, or plasticizers of the above mentioned type.

Microscopic examinations of blushed film as obtained by the process described below shows that the film contains numerous microscopic bubbles throughout the entire body. These very small hollow spaces give the a light appearance called blushing,- white if the layer is undy'ed In order to make the blushing disappear from the coating thus rendering the latter visible, it is merely necessary to eliminate the minute bubbles throughout the resin. The blushing obtained according to this invention difiers from that which involves actual inclusion of water. The blushing which is thus produced and maintained on varnished and shellaced surfaces by actual presenccof water does not disappear upon the application of heator pres-sure, but only uponremoval. of the water on the other hand, the blushing according to the invention although it will not disappear One prolonged ex p'osure to dehydrating: conditions because is not caused by the presence of water, responds .to the application or heat but not to pressure of degrees corresponding to usual accidental contact with astylus or other apparatus components.

Blushed coatings according to theinvention may be prepared by dissolving resin, more particularly film forming thermoplastic linear polymeric resin, in aa solvent-having a vapor pressure in excess of that or water and further diluting the resin solution with water, or a water-solvent mixture. The solvent must be one which is miscible with water while the resin must be substantially insoluble in water. If enough water is added to a solution of a resin, the resin will precipitate, therefore less water than is required to precipitate the resin should be added. If the desired recording temperature, preferably applied with a stylus or similar device, is fairly high depending on the solid constituent used, the solution is prepared free from any plasticizing addition. For adjustably lowering the recording temperature, a plasticizer of the particular type to be discussed isadded in variable amounts, depending upon the desired marking temperature of the stylus.

The water containing solution obtained as described above is applied to a suitable support such as paper in the form of a thin film, by roller coating, spraying, printing, floatin but prefer ably by a knife coating process. Acetone, a preferred solvent, may be employed, which evaporates and precipitates the resinalmost immediately after coating in the form of a white surface.

For the purpose of providing an easily readable record, the blushed film is preferably placed uponcolored, such as red or black, paper. When so placed, a'heated stylus applied lightly to the surface of the coating will cause a red or a black line to appear. However, it is not necessary to use colored paper. A dye may be incorporated in the film mixture which, upon deposition on the paper, will assume a light color of the hue of the dye. When marked with the heated stylus, a line of darker color of the same hue is produced.

Several resinous materials which blush in an acetone-water solution include ethyl cellulose, cellulose acetate, cellulose nitrate, cellulose caprate, cellulose acetate-propionate, cellulose acetate-butyrate, benzyl cellulose, polymethyl methacrylate and polystyrene.

As mentioned above the marking temperature of film entirely lacking a plasticizer is rather high, especially if cellulose acetate is used as solid component. It was found that this temperature may be lowered to predeterminable degrees without impairing the desirable high pressure insensitivity, if selected amounts of plasticizers of the primary type are added which are solvents for the film forming material and which have a vapor pressure lower than approximately that of diethyl phthalate, that is about 2.0 mm. at 150 C. Dibutyl phthalate, having a vapor pressure of 1.1 mm. was found to be very suitable. Plastieizers of the secondary, mechanical or lubricant type, such as glycerin, fatty acids, salts or esters of such acids or other oily, fatty or waxy materials, although they might affect the pressure sensitivity, are of no value for adjusting the temperature sensitivity of the blushed film.

The range of temperatures which are opera- 7 tive with blushed material of this type is between about 80 F. and 340 F.; the blushing will disappear when a stylus heated to a temperature :Withln this range is applied to the coating, thus ,causing avisible andclearly defined mark. Because the resins named above do not have sharp melting points, it is not necessary to heat them .to their melting point. Ethyl cellulose, for in- As primary plasticizers according to the invention, dioctyl phthalate was found to be very efiective with ethyl cellulose, but also tricresyl phosphate, diamyl phthalate, dicapryl phthalate, dibutoxyethyl phthalate, tributyl citrate, butyl phthalyl butyl glycolate and dibutyl sebacate; with cellulose acetate, ortho and paratoluene ethyl sulfonamide is effective but also such primary plasticizers as methyl phthalyl ethyl glycocolate or methoxyethyl phthalate.

These and other objects, aspects and features are further illustrated by the following examples of practical embodiments of the invention.

Example I Dissolve:

Grams Ethyl cellulose N- 10 Acetone 90 Add:

Di-Q-ethylhexyl phthalate 1.5 Acetone (50% solution in water) 40 Example II Dissolve:

Grams Ethyl cellulose 10 Acetone 52.5

Add to this solution:

Acetone 37.5 Water 15.0

Apply the resulting solution to red paper in a thin film and dry. The white, glossy film produced is quite adhesive and marks at C.

The addition of 2.5 grams of dioctyl phthalate (known to the trade as D O P) to the acetoneethyl cellulose solution lowers the marking point to 80 C.

Example III Dissolve: Grams Cellulose acetate 15 I -Acetone 60 To this solution add: Acetone 25 'Water 30 stance, has a melting point of 220C. and a mark- The resulting solution is applied to red paper in a thin film and dried. The film is white and glossy and marks at 170 C. The addition of 2.5 grams of a mixture of ortho and para toluene ethyl sulfonamide (known to the trade as Santicizer 8) lowers the marking temperature at C.

Example IV Dissolve: Grams Methyl methacrylate 20 in Acetone '70 To this solution add:

Acetone Water 5 Apply to a support as before; the marking point is 139 C.

Example V To the composition of Example II, add 0.5 gram of the dye National oil black 34341. The resulting solution is coated on white paper. The coating is light lavender in color and marks with a deeper color to give a distinct line. The marking point is 120 C.

It should be understood that the present disclosure is for the purpose of illustration only and that this invention includes all modifications and equivalents which fall within the scope of the appended claims.

I claim:

1. A heat-sensitive, dry, non-tacky recording material comprising a backing having an opaque blushed coating characterized by the presence therein of numerous microscopic hollow spaces, said coating consisting essentially of a water insoluble film-forming thermoplastic material selected from the group consisting of cellulose esters and ethers, polymethyl methacrylate and polystyrene and from to about 33% of a compatible primary plasticizer having a vapor pressure lower than about 2.0 mm. at 150 0., said coating being free from secondary plasticizers and substantially insensitive to pressure, but capable of becoming translucent in response to heat received from a stylus heated to a temperature of at least 80 (7., thereby to provide a visible contrast with the surrounding opaque unheated area.

2. A heat-sensitive material as defined in claim 1, further characterized in that said thermoplastic film-forming material consists essentially of cellulose acetate.

3. A heat-sensitive material as defined in claim 1, further characterized in that said thermoplastic film-forming material consists essentially of cellulose acetate and a toluene alkyl sulfonamide plasticizer.

4. A heat-sensitive material as defined in claim 1, further characterized in that said thermoplastic film-forming material consists essentially of ethyl cellulose.

5. A heat-sensitive material as defined in claim 1, further characterized in that said thermoplastic film-forming material consists essentially of ethyl cellulose and a compatible alkyl phthalate plasticizer.

6. A heat-sensitive material as defined in claim 1, further characterized in that said thermoplastic film-forming material consists essentially of methyl methacrylate.

RAYMOND W. JAMES.

REFERENCES CITED The following references are of record in the file of this patent:

New York, 1943 pages 258, 262, 268. 

1. A HEATING-SENSITIVE, DRY, NON-TACKING RECORDING MATERIAL COMPRISING A BACKING HAVING AN OPAQUE BLUSED COATING CHARACTERIZED BY THE PRESENCE THEREIN OF NUMEROUS MICROSCOPIC HOLLOW SPACES, SAID COATING CONSISTING ESSENTIALLY OF A WATER INSOLUBLE FILM-FORMING THERMOPLASTIC MATERIAL SELECTED FROM THE GROUP CONSISTING OF CELLULOSE ESTERS AND ETHERS, POLYMETHYL METHACRYLATE AND POLYSTYRENE AND FROM 15% TO ABOUT 33% OF A COMPATIBLE PRIMARY PLASTICIZER AHVING A VAPOR PRESSURE LOWER THAN ABOUT 2.0 MM. AT 150*C., SAID COATING BEING FREE FROM SECONDARY PLASTICIZERS AND SUBSTANTIALLY INSENSITIVE TO PRESSURE, BUT CAPABLE OF BECOMING TRANSLUCENT TO RESPONSE TO HEAT RECEIVED FROM A STYLUS HEATED TO A TEMPERATURE OF AT LEAST 80*C., THEREBY TO PROVIDE A VISIBLE CONTRAST WITH THE SURROUNDING OPAQUE UNHEATED AREA. 